I agree that AC might be your best choice especially if you do a lot of flying in North America and specifically between USA and Canada. I have always covered myself by being both an AC Super Elite and UA PremEX and find that both these carriers offer the best of all worlds. One extremely good feature of the AC Aeroplan is the availability of short haul flights for 15000 miles. This is a real deal. Take a look at the AC short haul flight chart. I also find that I don't have any problems getting reward flights, either Star alliance or AC with a little advance planning. Being AC gold will also give you free access to Maple Leaf lounges and all star alliance lounges.